Radial tilt reduced media

ABSTRACT

A storage media having a radial deviation of less than or equal to about 1.15 degrees at a radius of 55 mm is disclosed. In one embodiment, the storage media comprises: a plastic substrate, an optical layer and a data storage layer disposed therebetween. A reflective layer is disposed between the data storage layer and the substrate.

CROSS REFERENCE TO RELATED APPLICATION

This application Claims the benefit of U.S. Provisional Application Ser.No. 60/316,126 filed Aug. 30, 2001, and U.S. Provisional ApplicationSer. No. 60/279,887 filed Mar. 29, 2001, which are incorporated hereinby reference.

BACKGROUND OF THE INVENTION

Optical, magnetic and magneto-optic media are primary sources of highperformance storage technology that enables high storage capacitycoupled with a reasonable price per megabyte of storage. Areal density,typically expressed as billions of bits per square inch of disk surfacearea (Gbits per square inch (Gbits/in²)), is equivalent to the lineardensity (bits of information per inch of track) multiplied by the trackdensity in tracks per inch. Improved areal density has been one of thekey factors in the price reduction per megabyte, and further increasesin areal density continue to be demanded by the industry.

In the area of optical storage, advances focus on access time, systemvolume, and competitive costing. Increasing areal density is beingaddressed by focusing on the diffraction limits of optics (usingnear-field optics), investigating three dimensional storage,investigating potential holographic recording methods and othertechniques.

Conventional polymeric data storage media has been employed in areassuch as compact disks (CD-ROM) and recordable or re-writable compactdisks (e.g., CD-RW), and similar relatively low areal density devices,e.g., less than about 1 Gbits/in², which are typically optical devicesrequiring the employment of a good optical quality substrate having lowbirefringence.

Referring to FIG. 1, a low areal density system 1 is illustrated havinga read device 3 and a recordable or re-writable storage media 5. Thestorage media 5 comprises conventional layers, including a data layer 7,dielectric layers 9 and 9′, reflective layer 11, and protective layer13. During operation of the system 1, a laser 15 produced by the readdevice 3 is incident upon the optically clear substrate 17. The laserpasses through the substrate 17, and through the dielectric layer 9, thedata layer 7 and a second dielectric layer 9′. The laser 15 thenreflects off the reflective layer 11, back through the dielectric layer9′, the data layer 7, the dielectric layer 9, and the substrate 17 andis read by the read device 3.

Conventionally, the above issues associated with employing firstsurface, including near field, techniques have been addressed byutilizing metal, e.g., aluminum, and glass substrates. These substratesare formed into a disk and the desired layers are disposed upon thesubstrate using various techniques, such as sputtering. Possible layersinclude reflective layers, dielectric layers, data storage layers andprotective layers. Once the desired magnetic layers have been added, thedisk may be partitioned into radial and tangential sectors throughmagnetic read/write techniques. Sector structure may also be addedthrough physical or chemical techniques, e.g. etching, however this mustoccur prior to the deposition of the magnetic layers.

As is evident from the fast pace of the industry, the demand for greaterstorage capacities at lower prices, the desire to have re-writabledisks, and the numerous techniques being investigated, further advancesin the technology are constantly desired and sought.

BRIEF SUMMARY OF THE INVENTION

Disclosed herein is a storage media having a radial deviation of lessthan or equal to about 1.15 degrees at a radius of 55 mm. In oneembodiment, the storage media comprises: a plastic substrate, an opticallayer and a data storage layer disposed therebetween. A reflective layeris disposed between the data storage layer and the substrate.

The above described and other features are exemplified by the followingfigures and detailed description.

DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, wherein like elements are numbered alike:

FIG. 1 is a cross-sectional illustration of a prior art low arealdensity system employing an optically clear substrate.

FIG. 2 is a cross-sectional illustration of a read/write system usingone possible embodiment of a storage media with a light incident on thedata storage layer without passing through the substrate, i.e., a firstsurface storage media.

FIG. 3 is a graphical illustration of curvature change induced by ahumidity set from 25° C. and 50% relative humidity (rh) to 25° C. and90% rh for two matched systems with different bonding schemes (i.e., PSAand ultraviolet (UV) curable adhesive).

FIG. 4 is a graphical illustration of dynamic curvature of a substrateduring desorption and adsorption.

FIG. 5 is a graphical illustration of the effect of thickness onstructure curvature range during absorption and subsequent desorption.

FIG. 6 is a curvature ratio contour map at a diffusion ratio of 1.5.

FIG. 7 is a curvature ratio contour map at a diffusion ratio of 1.0.

FIG. 8 is a graphical illustration of curvature change induced by ahumidity set from 25° C. and 50% relative humidity (rh) to 25° C. and90% rh for a mismatched system (e.g., same substrate as FIG. 3 with adifferent composition film than substrate).

DETAILED DESCRIPTION OF THE INVENTION

In this specification and in the Claims that follow, reference will bemade to a number of terms that shall be defined. For example, thesingular forms “a”, “an” and “the” include plural referents unless thecontext clearly dictates otherwise. “Optional” or “optionally” mean thatthe subsequently described event or circumstance may or may not occur,and that the description includes instances where the event orcircumstance occurs and instances where it does not. “Tilt” as usedherein refers to the degrees by which a material bends on a horizontalaxis and is typically measured as the vertical deviation at the outerradius of the storage medium. The “maximum radial tilt range” as usedherein is the disk curvature during absorption and subsequent desorptionof water and is hence twice the radial tilt specification as usuallyspecified by the developers in the industry.

High-density re-recordable optical media formats are being developed toreplace existing VHS rape recorders for consumer entertainmentconsumption. The goal is to produce a removable media format approachingor even exceeding 20 gigabytes (GB) in storage and having data transferrates of shout 35 megabytes per second (MBps) and approaching or evenexceeding 100 (MBps). Thinner readthrough mediums are required for thesetypes of media with as thin as 80 micrometers currently are beingdeveloped. Most of the formats are asymmetric in structure with theabove mentioned thin readthrough medium being supported by a thickersubstrate. Curvature in the readthrough medium is induced by changes inthe surrounding environment. Humidity and temperature changes willinduce curvature into the total asymmetric structure end hence thereadthrough medium. The curvature induces spherical aberrations thatlead to poor performance of the optical drive. Disclosed below areranges of material parameters and material parameter ratios for thesubstrate and film that lead to improved dimensional stability of thetotal structure. This technology minimizes curvature variation in thereadthrough medium induced by environmental humidity changes.

Optical media format developers are currently moving towardsre-recordable optical media formats that will replace the consumer VHSmarket. In these formats the areal density is increased by: adding extrainformation layers, decreasing laser wavelength, and/or increasingnumerical aperture.

Both increasing the numerical aperture and decreasing the wavelength hasa detrimental impact on the magnitude of the optical aberrations andhence read noise/errors. These aberrations are considerably sensitive totilt of the optical medium. Materials utilized for manufacture ofoptical media generally adsorb water that in turn causes a volume changeof the material better known as swell. Any asymmetry in the waterabsorption/swell will incur a bending moment within the media. Asymmetryin the water absorption in optical disks is caused by the need forimpermeable metallic and inorganic layers adjacent to the informationlayer. The bending moment causes curvature in the media and hence thereadthrough medium.

Disc curvature is determined by measuring a laser beam deflection offthe disc surface. The angle of inclination from a flat horizontal discis compared to the angle of inclination of the disc of interest; thedifference in the angles is referred to as disc tilt. From geometricalconsiderations the laser beam deflection is equal to twice the disc tiltand is commonly referred to as radial deviation. The tilt range isdefined as the maximum range in the tilt measured on a disc at aspecific disc radius on both absorption and subsequent desorption ofwater.

To attain high areal densities in optical storage media the laser beamspot diameter (i.e., the diameter of the laser light beam that strikesthe media) needs to be decreased. In the pure diffraction limited casethe beam diameter is related to the numerical aperture and wavelength inthe following way:

${{Beam}\mspace{20mu}{Spot}\mspace{20mu}{Diameter}} \propto \left\lbrack \frac{\lambda}{N\; A} \right\rbrack$$\begin{matrix}{{{where}{~~~~}\lambda} = {wavelength}} \\{{NA} = {{numerical}\mspace{20mu}{aperture}}}\end{matrix}$

In the optical media formats laser wavelength and/or numerical aperturemay be altered to achieve the desired density increase. The inherentproblem with moving to lower wavelengths and higher numerical aperturesis the retrospective noise tolerance collapse; e.g., tilt tolerance,which is related to the above in the following way:

${{Tilt}\mspace{20mu}{Margin}} \propto \left\lbrack \frac{\lambda}{{d \cdot N}\; A^{3}} \right\rbrack$where  d = thickness  of  readthrough  medium

In media formats being developed the thickness of the optical medium isbeing reduced, relative to current formats, to increase the disc tilttolerance. This optical layer or optical film is then bonded to athicker substrate for mechanical stability and final use in an opticaldrive. There are other instances where more than one of these opticallayers is bonded together to obtain a multilayer format similar to theDVD format. The film is the optical medium and the information layer ison the injection-molded substrate. These thin optical mediums can bethought of as optical films.

Referring to FIG. 2, for example, data retrieval comprises contactingthe data storage layer(s) 102 (e.g., surface features, phase changematerial, or organic dye) with a light beam 110 (white light, laserlight, or other) incident on such layer(s). A reflective layer (notshown), disposed between the data storage layer 102 and substrate 108,reflects the light back through the data storage layer 102, adhesivelayer 106, optical layer 114, and to the read/write device 112 where thedata is retrieved.

Assuming that the structure is an elastic plate that extends infinitelyin the in-plane directions and that the material properties are not afunction of thickness then the isotropic strain due to water absorptionis given by the below expression:

${\overset{\_}{ɛ}(t)} = {\frac{\beta}{l}{\int\limits_{l/2}^{{- l}/2}{{c\left( {z,t} \right)}{\mathbb{d}z}}}}$$\begin{matrix}{{{where}:ɛ} = {strain}} \\{z = {{thickness}\mspace{20mu}{direction}}} \\{l = {thickness}} \\{c = {concentration}} \\{\beta = {{{swell}\mspace{20mu}{coefficient}\mspace{20mu}{where}\mspace{20mu}{ɛ(t)}} = {\beta\;{c\left( {z,t} \right)}}}}\end{matrix}$

The curvature of the substrate is related to the first moment of thewater distribution in the disk as shown below:

${\kappa(t)} = {\frac{12\beta}{l}{\int\limits_{l/2}^{{- l}/2}{{c\left( {z,t} \right)}z{\mathbb{d}z}}}}$

For multiple layer systems the above integrals are summations ofintegrals across the specific layer thicknesses including materialparameters for each layer. The concentration of water as a function ofthickness and time c(z,t) is calculated from a solution to the diffusionequation. In the case of a two layer system the time dependant curvaturechange induced by a set humidity change is given by the below generalexpression:

${{\kappa(t)} - {\kappa(0)}} = {\frac{6{\Delta\phi\beta}_{1}s_{1}}{l_{1}}{f\left( {{t;\rho},\gamma,\delta\;,q} \right)}}$where t=time

Δφ=change in relative humidity

${\rho = {\frac{l_{2}}{l_{2}} = {{ratio}\mspace{20mu}{of}\mspace{20mu}{layer}\mspace{20mu}{thickness}}}},$

${\gamma = {\frac{\frac{E_{2}}{1 - v_{2}}}{\frac{E_{1}}{1 - v_{1}}} = {{ratio}\mspace{20mu}{of}\mspace{20mu}{mechanical}\mspace{20mu}{stiffness}}}},$

${\delta = {\frac{\beta_{2}s_{2}}{\beta_{1}s_{1}} = {\frac{ɛ_{2}^{\infty}}{ɛ_{1}^{\infty}} = {{ratio}\mspace{20mu}{of}\mspace{20mu}{water}\mspace{20mu}{strains}}}}},$

$q = {\frac{D_{2}}{D_{1}} = {{ratio}\mspace{20mu}{of}\mspace{20mu}{diffusivities}}}$subscript “2” refers to the film and subscript “1” refers to thesubstrate

If all of the material parameters are supplied, the two layer structuredynamic curvature change can be determined. FIG. 3 exhibits validationwith the above mathematical description and experimental data on: amatched optical film/substrate polycarbonate system (e.g., a systemcomprising a polycarbonate optical film and a polycarbonate substrate)that under went a step in environmental humidity. Meanwhile, FIG. 4exhibits further validation on three different systems with variousbonding layers and both matched and mismatched systems.

Optical media manufacturers specify upper and lower specification limitson structure curvature. This requires that the substrate curvature fallswithin these specification limits at all times during any environmentalhumidity change. The curvature range (FIG. 5) during an absorption andsubsequent desorption should be minimized. There are three ways toreduce the curvature range: (1) reduce the swell/strain of the substrateon absorption of water, (2) select a film that minimizes the curvaturedynamic of the structure, and (3) change the film thickness. Anexplanation of how to reduce the curvature or tilt range of a singlelayer substrate or a dual layer system by selecting materials withreduced swell/strain on absorption of water is set forth in commonlyassigned U.S. patent Ser. No. 09/943,767.

The maximum in the dynamic curvature on absorption and desorption ofwater for a single substrate is given by the following relation:

${{\kappa(t)} - {\kappa(0)}} = \frac{6{\Delta\phi\beta}_{1}s_{1}}{l_{1}}$This shows that reducing the solubility and swell coefficient of thematerial can minimize the pure substrate tilt. Consequently, an opticalfilm is chosen to minimize system curvature. The curvature can beconverted into a tilt and the maximum tilt range experienced by thestructure on sorption and subsequent desorption is given by the belowexpression:

${{Max}\mspace{14mu}{Radial}\mspace{14mu}{Tilt}\mspace{14mu}{Range}\mspace{14mu}({rad})} = {{\kappa\; r} = {\frac{1.92\Delta\;{rh}\;\beta\;{sr}}{t} = {\frac{1.92\Delta\;{rh}\; ɛ\; r}{t}\begin{matrix}{{{where}\text{:}\kappa\mspace{14mu}{is}\mspace{14mu}{the}\mspace{14mu}{curvature}\mspace{14mu}\left( {length}^{- 1} \right)};} \\{{\Delta\;{rh}{\mspace{11mu}\;}{is}\mspace{14mu}{step}\mspace{14mu}{relative}\mspace{14mu}{humidity}};} \\{{\beta\mspace{14mu}{is}\mspace{14mu}{strain}\text{/}{mass}\mspace{14mu}{fraction}\mspace{14mu}{water}\mspace{14mu}{at}\mspace{14mu} a\mspace{14mu}{given}\mspace{14mu}{temperature}\mspace{14mu}(T)};} \\{{{s\mspace{14mu}{is}\mspace{14mu}{mass}\mspace{14mu}{fraction}\mspace{14mu}{water}\mspace{14mu}{at}\mspace{14mu}{relative}\mspace{14mu}{humidity}\mspace{14mu}({rh})} = {1\mspace{14mu}{and}\mspace{14mu} T}};} \\{{ɛ = {{\beta\; s\mspace{14mu}{is}\mspace{14mu}{water}\mspace{14mu}{strain}\mspace{14mu}{at}\mspace{14mu}{rh}} = {1\mspace{14mu}{and}\mspace{14mu} T}}};} \\{{t\mspace{14mu}{is}\mspace{14mu}{substrate}\mspace{14mu}{thickness}};{a\;{nd}}} \\{r\mspace{14mu}{is}\mspace{14mu}{radius}\mspace{14mu}{of}\mspace{14mu}{{interest}.}}\end{matrix}}}}$The “maximum radial tilt range” as used herein is the disk curvatureduring absorption and subsequent desorption of water and is hence twicethe radial tilt specification as usually specified by the developers inthe industry.

FIG. 4 outlines the dynamic curvature in absorption and subsequently indesorption normalized by

$\frac{6\Delta\;{\phi\beta}_{1}s_{1}}{l_{1}}$hence arriving at a value of one and minus one at the maximum andminimum respectively for a substrate without film. By adding a filmcomprising a different chemical composition than the substrate, theasymmetry can be reduced, hence reducing the value of the maximum tilt.

As the thickness of the optical film (matching film and mismatched film)is increased, the maximum tilt will also reduce to the point where thereis no tilt for a film of the same thickness as the substrate (e.g., DVD,DVR (digital video recordings), and the like). FIG. 5 exhibits thebehavior of the curvature range with the thickness ratio where the filmand substrate are the same material. It was disclosed that by having amatched film that is approximately 30% of the thickness of thesubstrate, the tilt of the coated substrate can be reduced to 5% of thatof a substrate without a film. Additionally at an optical film (layer)thickness of about 20% of the substrate thickness the tilt reduction isdown to 10% of the substrate tilt. This curvature dependence onthickness is stronger than the tilt tolerance reduction caused byaberrations dependence on thickness. Consequently, by having an opticalfilm thickness of greater than or equal to about 18% of the substratethickness, the tilt can be reduced by greater than or equal to about80%, with a reduction in tilt of greater than or equal to about 90%obtained with an optical film thickness of greater than or equal toabout 20% of the substrate thickness. Preferably, the optical filmthickness is about 20% to about 40% of the substrate thickness, with athickness of about 25% to about 35% of the substrate thicknesspreferred.

If the thickness of the film is fixed then material properties of thefilm can be optimized to reduce the tilt range. By mismatching thematerial of the film to that of the substrate, the tilt range can alsobe reduced. For example, Table 1 gives ratios of parameters for a discsystem (100 micrometer (μm) film and 1.1 millimeter (mm) substrate) thatlead to a curvature range that is 11% that of the substrate curvaturerange. This is a four fold improvement over a matched film/substratesystem for a given thickness.

TABLE 1 Ratios Value Thickness ρ 0.09 Stiffness γ 3   Swell δ 1.01Diffusivity q 0.15 Minimum Range 0.11

For a given film thickness the curvature is more sensitive to the strainratio and stiffness ratio and less sensitive to the diffusion ratio.FIG. 6 is a contour plot outlining the normalized curvature range as afunction of the stiffness ratio and strain/swell ratio. This contourplot is for a specific diffusion ratio of 1.5. The optimum curvaturerange is obtained for the case where the stiffness ratio is related tothe strain ratio in a hyperbolic way. This hyperbolic functionality isconsistent for any diffusion ratio as is supported by FIG. 7, whichillustrates contour plot for a specific diffusion ratio of 1.0.Preferably, the stiffness ratio to swell ratio is within the innercontour by area 200.

Based upon the above information, the optical film can be a plastichaving the desired stiffness ratio (γ) (Youngsmodulus(megapascals)/(1-Poisson ratio)), swell ratio(δ) (percentagegrowth of the material at equilibrium), and diffusivity ratio(q),wherein all ratios refer to the ratio of the optical film to thesubstrate. The desired amounts of these parameters are dependent uponthe thickness of the optical film. The ultimate desire is to reduce thetilt, e.g., curvature, to a radial deviation range of less than or equalto about 1.15 degrees at a radius of 55 mm, with less than or equal toabout 1.0 degrees at a radius of 55 mm preferred, less than or equal toabout 0.80 degrees at a radius of 55 mm more preferred, less than orequal to about 0.70 degrees at a radius of 55 mm even more preferred,less than or equal to about 0.50 degrees at a radius of 55 mm yet evenmore preferred, and less than or equal to about 0.25 degrees at a radiusof 55 mm desired. Generally, the stiffness ratio can be greater than orequal to about 0.5, with a stiffness ratio of greater than or equal toabout 0.70 preferred, and a stiffness ratio of greater than or equal toabout 1.25 more preferred. Preferably, the stiffness ratio is less thanor equal to about 5, with a stiffness ratio of less than or equal toabout 3 preferred, and a stiffness ratio of less than or equal to about2.5 even more preferred. The stiffness of the optical film and substrateis measured in tensile deformation at room temperature using an Instrontesting machine. With respect to the swell ratio, it can be greater thanor equal to about 0.50, with greater than or equal to about 0.75preferred, and greater than or equal to about 1.0 more preferred.Preferably, the swell ratio is less than or equal to about 5, with lessthan or equal to about 3 more preferred, and less than or equal to about2.5 even more preferred. The swell strain is measured using aThermomechanical analyzer from TA instruments. The diffusivity ratio canbe greater than or equal to about 0.05, with greater than or equal toabout 0.10 preferred. Preferably the diffusivity is less than or equalto about 2.0, with less than or equal to about 1.0 preferred

With respect to thickness, the optical film can have a thickness ofabout 0.2 micrometers to about 0.6 mm. Within the film thickness range,less than or equal to about 0.6 mm is preferred, less than or equal toabout 250 micrometers is more preferred, and less than or equal to about120 micrometers is even more preferred, in some applications. Alsopreferred within this range is the optical thickness of greater than orequal to about 0.2 micrometers, with greater than or equal to about 5micrometers more preferred, and greater than or equal to about 50micrometers even more preferred. In contrast, the substrate typicallyhas a thickness of greater than or equal to about 0.3 mm, with greaterthan or equal to about 0.6 mm preferred, and greater than or equal toabout 1.1 mm more preferred. Also preferred is a substrate thickness ofless than or equal to about 2.5 mm, with less than or equal to about 2.0mm more preferred, and less than or equal to about 1.5 mm even morepreferred. Due to current equipment and due to industry specifications,a substrate thickness of about 1.1 mm is generally preferred. Ifdecreased substrate thicknesses are employed (e.g., less than about 1.2mm), it is preferred to maintain a optical film to substrate thicknessratio of less than or equal to about 1, with a thickness ratio of lessthan or equal to about 0.5 preferred, and less than or equal to about0.1 more preferred. Also preferred is a thickness ratio of greater thanor equal to about 0.001, with greater than or equal to about 0.005 morepreferred, and greater than or equal to about 0.025 even more preferred.

Possible optical film materials that can be any plastic that exhibitsappropriate properties, including thermoplastics, thermosets, as well ashomopolymers, copolymers, reaction products, and combinations comprisingat least one of the foregoing materials including, but not limited toaddition and condensation polymers. Illustrative, non-limiting examplesof thermoplastic polymers are olefin-derived polymers such aspolyethylene, polypropylene, and their copolymers; chlorinatedpolyethylene, polyvinyl chloride, polymethylpentane;ethylene-tetrafluoroethylene copolymers, polyvinyl fluoride,polyvinylidene fluoride, polyvinylidene chloride,polytetrafluoroethylene, ethylene-vinyl acetate copolymers, polyvinylacetate, diene-derived polymers such as polybutadiene, polyisoprene, andtheir copolymers; polymers of ethylenically unsaturated carboxylic acidsand their functional derivatives, including acrylic polymers such aspoly(alkyl acrylates), poly(alkyl methacrylates), polyacrylamides,polyacrylonitrile and polyacrylic acid; alkenylaromatic polymers such aspolystyrene, poly-alpha-methylstyrene, hydrogenated polystyrenes,syndiotactic and atactic polystyrenes, polycyclohexyl ethylene,styrene-co-acrylonitrile, styrene-co-maleic anhydride, polyvinyltoluene,and rubber-modified polystyrenes; polyamides such as nylon-6, nylon-66,nylon-11, and nylon-12; polyacetals, polyesters such as polyethyleneterephthalate, polybutylene terephthalate, and polycyclohexylmethyleneterephthalate; polycarbonates; polyestercarbonates; high heatpolycarbonates, polyethers such as polyarylene ethers especiallypolyphenylene ethers derived from 2,6-dimethylphenol and copolymers with2,3,6-trimethylphenol, polyethersulfones, polyetherethersulfones,polyetherketones, polyetheretherketones, and polyetherimides;polyarylene sulfides, polysulfones, and polysulfidesulfones; and liquidcrystalline polymers.

Non-limiting examples of thermosetting resins are epoxies, phenolics,alkyds, polyesters, polyimides, polyurethanes, mineral filled silicones,bis-maleimides, cyanate esters, multifunctional allylic compounds suchas diallylphthalate, acrylics, alkyds, phenol-formaldehyde, novolacs,resoles, bismaleimides, PMR resins, melamine-formaldehyde,urea-formaldehyde, benzocyclobutanes, hydroxymethylfurans, andisocyanates benzocyclobutene resins, as well as homopolymers,copolymers, reaction products, and combinations comprising at least oneof the foregoing thermosetting resins. In one embodiment, the thermosetpolymer further comprises at least one thermoplastic polymer, such as,polyphenylene ether, polyphenylene sulfide, polysulfone, polyetherimide,polyester, and the like, as well as homopolymers, copolymers, reactionproducts, and combinations comprising at least one of the foregoingthermoplastic polymers. The thermoplastic polymer is typically combinedwith a thermoset monomer mixture before curing of the thermoset.

Both thermoplastic polyesters and thermoplastic elastomeric polyesterscan be employed. Illustrative, non-limiting examples of thermoplasticpolyesters include poly(ethylene terephthalate), poly(1,4-butyleneterephthalate), poly(1,3-propylene terephthalate),poly(cyclohexanedimethanol terephthalate),poly(cyclohexanedimethanol-co-ethylene terephthalate), poly(ethylenenaphthalate), poly(butylene naphthalate), and polyarylates.Illustrative, non-limiting examples of thermoplastic elastomericpolyesters (commonly known as TPE) include polyetheresters such aspoly(alkylene terephthalate)s (particularly poly[ethylene terephthalate]and poly[butylene terephthalate]) containing soft-block segments ofpoly(alkylene oxide), particularly segments of poly(ethylene oxide) andpoly(butylene oxide); and polyesteramides such as those synthesized bythe condensation of an aromatic diisocyanate with dicarboxylic acids anda carboxylic acid-terminated polyester or polyether prepolymer.

Suitable polyarylates include, but are not limited to, the polyphthalateesters of 2,2-bis(4-hydroxyphenyl)propane (commonly known as bisphenolA), and polyesters consisting of structural units of the formula I:

wherein R¹⁶ is hydrogen or C₁₋₄ alkyl, optionally in combination withstructural units of the formula II:

wherein R¹⁷ is a divalent C₄₋₁₂ aliphatic, alicyclic or mixedaliphatic-alicyclic radical. The latter polyesters may be prepared bythe reaction of a 1,3-dihydroxybenzene moiety with at least one aromaticdicarboxylic acid chloride under alkaline conditions. Structural unitsof formula II contain a 1,3-dihydroxybenzene moiety which may besubstituted with halogen, usually chlorine or bromine, or preferablywith C₁₋₄ alkyl; e.g., methyl, ethyl, isopropyl, propyl, butyl. Thealkyl groups are preferably primary or secondary groups, with methylbeing more preferred, and are most often located in the ortho positionto both oxygen atoms although other positions are also contemplated. Themost preferred moieties are resorcinol moieties, in which R¹⁶ ishydrogen. The 1,3-dihydroxybenzene moieties are linked to aromaticdicarboxylic acid moieties which may be monocyclic moieties, e.g.,isophthalate or terephthalate, or polycyclic moieties, e.g.,naphthalenedicarboxylate.

In the optional soft block units of formula II, resorcinol oralkylresorcinol moieties are present in ester-forming combination withR¹⁷ which is a divalent C₄₋₁₂ aliphatic, alicyclic or mixedaliphatic-alicyclic radical.

Possible polycarbonates include those comprising structural units of theformula III:

wherein at least about 60 percent of the total number of R¹⁸ groups arearomatic organic radicals and the balance thereof are aliphatic,alicyclic, or aromatic radicals. Suitable R¹⁸ radicals includem-phenylene, p-phenylene, 4,4′-biphenylene,4,4′-bi(3,5-dimethyl)-phenylene, 2,2-bis(4-phenylene)propane,6,6′-(3,3,3′,3′-tetramethyl-1,1′-spirobi[1H-indane]),1,1′-bis(4-phenylene)-3,3,5-trimethylcyclohexane, and similar radicalssuch as those which correspond to the dihydroxy-substituted aromatichydrocarbons disclosed by name or formula (generic or specific) in U.S.Pat. No. 4,217,438.

More preferably, R¹⁸ is an aromatic organic radical and still morepreferably a radical of the formula IV:—A¹—Y¹—A—  (IV)wherein each A¹ and A² is a monocyclic divalent aryl radical and Y¹ is abridging radical in which one or two atoms separate A¹ and A². Forexample, A¹ and A² typically represent unsubstituted phenylene orsubstituted derivatives thereof. The bridging radical Y¹ is most often ahydrocarbon group and particularly a saturated group such as methylene;cyclohexylidene; 3,3,5-trimethylcyclohexylidene; or isopropylidene. Themost preferred polycarbonates are bisphenol A polycarbonates, in whicheach of A¹ and A² is p-phenylene and Y¹ is isopropylidene. Suitablepolycarbonates may be made using various processes, includinginterfacial, solution, solid state, or melt processes.

In one embodiment, the storage media comprises at least one layer withat least one polycarbonate. In another embodiment, the storage mediacomprises at least one layer with two different polycarbonates.Homopolycarbonates derived from a single dihydroxy compound monomer andcopolycarbonates derived from more than one dihydroxy compound monomerare encompassed.

In one embodiment, the substrate and/or at least one other layer of thestorage media comprise a polycarbonate or copolycarbonate comprisingstructural units (V) or (VI):

where R¹, R², R³, R⁴, R⁵, and R⁶ are, independently chosen from C₁–C₆alkyl and hydrogen; R⁷ and R⁸ are, independently, C₁–C₆ alkyl, phenyl,C₁–C₆ alkyl substituted phenyl, or hydrogen; m is an integer of 0 toabout 12; q is an integer of 0 to about 12; m+q is an integer of about 4to about 12; n is an integer of about 1 to about 2; and p is an integerof about 1 to about 2.

Representative units of structure (V) include, but are not limited, toresidues of 1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane (DMBPC);1,1-bis(4-hydroxy-3 -methylphenyl)cyclopentane;1,1-bis(4-hydroxy-3-methylphenyl)cycloheptane;1,1-bis(4-hydroxy-3-methylphenyl)-3,3,5-trimethylcyclohexane (DMBPI);and mixtures comprising at least one of the foregoing units.

Representative units of structure (VI) include, but are not limited, toresidues of 2,2-bis(4-hydroxy-3-methyl)propane (DMBPA); and 4,4′-(1-phenylethylidene)bis(2-methylphenol) (DMbisAP).

In an even further embodiment, the substrate and/or at least one otherlayer of the storage media can comprise polycarbonate or copolycarbonatecomprises structural units (VII):

where R⁹, R¹⁰, R¹³ and R¹⁴ are independently C₁–C₆ alkyl, R¹¹ and R¹²are independently H or C₁–C₅ alkyl, each R is independently selectedfrom H and C₁–C₃ alkyl and each n is independently selected from 0, 1and 2.

Representative units of structure (VII) include, but are not limited to,6,6′-dihydroxy-3,3,3′,3′-tetramethyl spirobiindane (SBI);6,6′-dihydroxy-3,3,5,3′,3′, 5′-hexamethyl spirobiindane;6,6′-dihydroxy-3,3,5,7,3′,3′,5′,7′-octamethylspirobiindane;5,5′-diethyl-6,6′-dihydroxy 3,3,3′,3′-tetramethylspirobiindane, andmixtures comprising at least one of the foregoing units.

The polyphenylene ethers are polymers comprising a plurality ofstructural units of the formula (VIII)

wherein in each of the units independently, each Q¹ is independentlyhalogen, primary or secondary lower alkyl (i.e., alkyl containing up to7 carbon atoms), phenyl, haloalkyl, aminoalkyl, hydrocarbonoxy, orhalohydrocarbonoxy wherein at least two carbon atoms separate thehalogen and oxygen atoms; and each Q² is independently hydrogen,halogen, primary or secondary lower alkyl, phenyl, haloalkyl,hydrocarbonoxy or halohydrocarbonoxy as defined for Q¹. Most often, eachQ¹ is alkyl or phenyl, especially C₁₋₄ alkyl, and each Q² is hydrogen.

Both homopolymer and copolymer polyphenylene ethers are can be employed.Suitable copolymers include random copolymers containing such units incombination with (for example) 2,3,6-trimethyl-1,4-phenylene etherunits. Also included are polyphenylene ethers containing moietiesprepared by grafting onto the polyphenylene ether in a known manner suchmaterials as vinyl monomers or polymers such as polystyrenes andelastomers, as well as coupled polyphenylene ethers in which couplingagents such as low molecular weight polycarbonates, quinones,heterocycles and formals undergo reaction in known manner with thehydroxy groups of two polyphenylene ether chains to produce a highermolecular weight polymer, provided a substantial proportion of free OHgroups remains.

Particularly useful polyphenylene ethers for many purposes are thosethat comprise molecules having at least one aminoalkyl-containing endgroup. The aminoalkyl radical is typically located in an ortho positionto the hydroxy group. Polymers containing such end groups may beobtained by incorporating an appropriate primary or secondary monoaminesuch as di-n-butylamine or dimethylamine as one of the constituents ofthe oxidative coupling reaction mixture. Also frequently present are4-hydroxybiphenyl end groups, typically obtained from reaction mixturesin which a by-product diphenoquinone is present, especially in acopper-halide-secondary or tertiary amine system. A substantialproportion of the polymer molecules, typically constituting as much asabout 90% by weight of the polymer, may contain at least one of theaminoalkyl-containing and 4-hydroxybiphenyl end groups.

It will be apparent that the contemplated polyphenylene ethers includeall those presently known, irrespective of variations in structuralunits or ancillary chemical features, including, but not limited tohomopolymer and copolymer thermoplastic polymers, and mixturescomprising at least one of the foregoing polyphenylene ethers.Copolymers may include random, block or graft type. Thus, for example,suitable polystyrenes include homopolymers, such as amorphouspolystyrene and syndiotactic polystyrene, and copolymers containingthese species. The latter embraces high impact polystyrene (HIPS), agenus of rubber-modified polystyrenes comprising blends and graftswherein the rubber is a polybutadiene or a rubbery copolymer of styrenein a range between about 70% by weight and about 98% by weight and dienemonomer in a range between about 2% by weight and about 30% by weight.Also included are ABS copolymers, which are typically grafts of styreneand acrylonitrile on a previously formed diene polymer backbone (e.g.,polybutadiene or polyisoprene). Suitable ABS copolymers may be producedby various methods.

In a preferred embodiment the optical film comprises thermoplasticresins and the substrate comprises thermosetting resins. It is alsopossible for the optical film to comprises thermosetting resins whilethe substrate comprises thermoplastic resins. Similarly it is possiblefor the optical film and the substrate to comprise a mixture ofthermoplastic and thermosetting resins and wherein at least one elementof the composition of the optical film is different from that of thesubstrate.

The optical layer or film can be deposited by a variety of techniques,including vapor deposition (e.g., plasma enhanced chemical vapordeposition, and the like), coating (e.g., electrodeposition coating,meniscus coating, spray coating, extrusion coating, spin coating,solution coating, and the like), casting (e.g., extrusion casting,solution casting, and the like), injection molding, film blowing,calendaring, and the like, as well as combinations comprising at leastone of the foregoing techniques. Meanwhile, the substrate is typicallymanufactured by an extrusion, molding (e.g., injection molding,extrusion molding, compression molding, and the like), and the like, aswell as combinations comprising at least one of the foregoingtechniques.

Although the substrate is typically a polycarbonate material, it isclearly understood that the substrate can also comprise any plasticmentioned above in relation to the optical film. For example, thesubstrate can comprise thermoplastics wherein the thermoplastic isbisphenol A polycarbonate, copolyester polycarbonate of bisphenol A anddodecanoic acid containing 7 mole % of polyester and 93 mole % ofbisphenol A polycarbonate, 39 mole % of polyphenylene ether and 61 mole% polystyrene, 1,3-bis(4-hydroxyphenyl methane), 90 mole % bisphenol Aand 10 mole % disecbutyl bisphenol A, polycarbonate of tetramethylcyclobutanediol and high flow polycarbonate tetra xylyl hydroquinonediphosphite, and the like, as well as mixtures comprising at least oneof the foregoing thermoplastics. Similarly, the optical layer cancomprise thermoplastics including 80 wt % isophthalate terephthalateresorcinol-20 wt % polycarbonate, styrene acrylonitrile, bisphenol Apolycarbonate, copolyester polycarbonate of bisphenol A and dodecanoicacid containing 7 mole % of polyester and 93 mole % of bisphenol Apolycarbonate, 39 mole % of polyphenylene ether and 61 mole %polystyrene, 1,3-bis(4-hydroxyphenyl methane), 90 mole % bisphenol A and10 mole % disecbutyl bisphenol A, polycarbonate of tetramethylcyclobutanediol and high flow polycarbonate tetra xylyl hydroquinonediphosphite, and the like, as well as reaction products and mixturescomprising at least one of the foregoing thermoplastics. Furthermore,the film for these high density formats preferably has opticalproperties such as in-plane retardations of less than or equal to about10 nanometers (nm). The films also have low thickness non-uniformity andsurface roughness. For a 100 micrometer film, thickness uniformity atlength scales longer than 2 centimeters (cm) is on the order of lessthan or equal to about 2 micrometers and the surface roughness at the 1millimeter (mm) length scale is on the order of less than or equal toabout 40 nm.

The substrate may further include energy absorption. Dampening can beachieved through a variety of approaches such as by addition of anenergy absorbing component or through slip mechanisms involving variousfillers and reinforcing agents. Useful materials that may improve thedamping characteristics include elastic materials with high dampingcapabilities (e.g., a damping coefficient of greater than or equal toabout 0.05), such as vulcanized rubbers, acrylic rubbers, siliconerubbers, butadiene rubbers, isobutylene rubbers, polyether rubbers,isobutylene-isoprene copolymers and isocyanate rubber, nitrile rubbers,chloroprene rubbers, chlorosulfonated polyethylene, polysulfide rubbersand fluorine rubber, block copolymers including polystyrene-polyisoprenecopolymers such as described in U.S. Pat. No. 4,987,194, thermoplasticelastomeric materials, including polyurethanes, and combinationscomprising at least one of the foregoing, among others.Vibration-damping materials also include resins in which large amountsof particles (such as ferrites, metals, ceramics, and the like), flakes(such as of talc, mica and the like), and various fibers (such as zincoxide, wollastonite, carbon fibers, glass fibers, and the like), andmixtures comprising at least one of the foregoing, can be employed.Microfibers, fibrils, nanotubes, and whiskers, foamed and honeycombedstructures may also be useful as are various combinations of theforegoing.

Beside the optical layer, which is typically the top layer, other layerswhich may be applied to the substrate may include one or more datastorage layer(s), lubricating layer(s), adhesive layer(s), dielectriclayer(s), reflective layer(s), insulating layer(s), combinationscomprising at least one of these layers, and others. The data storagelayer(s) may comprise any material capable of storing retrievable data,such as an optical layer, magnetic layer, or more preferably amagneto-optic layer, having a thickness of less than or equal to about600 Å, with a thickness of less than or equal to about 300 Å preferred.Possible data storage layers include, but are not limited to, oxides(such as silicone oxide), rare earth element—transition metal alloy,nickel, cobalt, chromium, tantalum, platinum, terbium, gadolinium, iron,boron, as well as alloys and combinations comprising at least one of theforegoing, and others, such as organic dye (e.g., cyanine orphthalocyanine type dyes), and inorganic phase change compounds (e.g.,TeSeSn or InAgSb). The data layer may comprise grooves, channels,projections, depressions, ruts, lands, protrusions, pits, etc. (“surfacefeatures”; see FIG. 2, data layer 102). Preferably, the data layer has acoercivity of greater than or equal to about 1,500 oersted, with acoercivity of greater than or equal to about 3,000 oersted especiallypreferred.

The dielectric layer(s) which are often employed as heat controllers,can typically have a thickness of up to or exceeding about 1000 Å and aslow as about 200 Å. Possible dielectric layers include nitrides (e.g.,silicon nitride, aluminum nitride, and others); oxides (e.g., aluminumoxide); carbides (e.g., silicon carbide); and combinations comprising atleast one of the foregoing dielectric layers, among other materialscompatible within the environment and preferably not reactive with thesurrounding layers.

The reflective layer(s) should have a sufficient thickness to reflect asufficient amount of energy to enable data retrieval. Typically thereflective layer(s) can have a thickness of up to and sometimesexceeding about 700 Å, with a thickness of about 300 Å to about 600 Ågenerally preferred. Possible reflective layers include any materialcapable of reflecting the particular energy field, including metals(e.g., aluminum, silver, gold, titanium, and alloys and mixturescomprising at least one of the foregoing materials and others). Thereflective layers may be disposed on the substrate by various techniquessuch as sputtering, chemical vapor deposition, electroplating and thelike.

Optionally disposed between the optical layer and the data storagelayer, and/or between other layers, is an adhesive layer that can, forexample, adhere the optical film to the other layers supported by thesubstrate. The adhesive layer can also be employed to enhance thedampening of the disc, with the thickness and nature of the adhesivedetermining the amount of dampening provided by the layer. The adhesivelayer, which can have a thickness of up to about 50 micrometers (μm) orso, with thicknesses of about 1 micrometers to about 30 micrometerspreferred, can comprise rubber based or elastomeric thermosets, flexiblethermoplastics, and the like. Typical adhesives are rubber-based orrubberlike materials, such as natural rubber or silicone rubber oracrylic ester polymers, and the like. Non-rigid polymeric adhesives suchas those based on rubber or acrylic polymers and the like have some ofthe properties of elastomers, such as flexibility, creep resistance,resilience, and elasticity, and do provide useful dampening to enhancethe quality of playback of the data storage disc. The chemistry ofnon-rigid polymeric adhesives is diverse, and includes polymers of thetypes of materials described herein as elastomers and rubbers, asflexible thermoplastics, and as thermoplastic elastomers. Suitableexamples of such adhesives include polyisoprene, styrene butadienerubber, ethylene propylene rubber, fluoro vinyl methyl siloxane,chlorinated isobutene-isoprene, chloroprene, chlorinated polyethylene,chlorosulfonated polyethylene, butyl acrylate, expanded polystyrene,expanded polyethylene, expanded polypropylene, foamed polyurethane,plasticized polyvinyl chloride, dimethyl silicone polymers, methyl vinylsilicone, polyvinyl acetate, and the like, as well as compositionscomprising at least one of the foregoing adhesives. This layer may alsocomprise any combination comprising at least one of the above adhesives.Typically pressure sensitive adhesives are preferred for use in datastorage disc applications. The adhesive layer may be added to the datastorage disc by methods such as vapor deposition, spin casting, solutiondeposition, injection molding, extrusion molding, and the like.

In addition to the data storage layer(s), dielectric layer(s),protective layer(s) and reflective layer(s), other layers can beemployed such as lubrication layer and others. Useful lubricants includefluoro compounds, especially fluoro oils and greases, and the like.

The storage media disclosed herein reduces tilt as compared to asubstrate without an optical layer and/or a substrate with a matchedoptical layer (e.g., where the optical layer comprises the same materialas the substrate) by controlling the thickness and/or mismatching theoptical layer and substrate compositions. Sonic of the advantages areillustrated in FIG. 8, which shows a substantial reduction in radialdeviation (i.e., a deviation of 0.50 degrees) versus the mismatchedsystem of FIG. 3 (e.g., a radial deviation of 1.26 degrees). Note, FIGS.3 and 8 employ the same substrate with different optical layers. In FIG.3, numbers 1–3 relate to samples comprising polycarbonate substrate andoptical layer with a pressure sensitive adhesive disposed therebetween,while samples 10, 20, 30, and 40 employ a polycarbonate substrate andoptical layer with a UV curable adhesive.

EXAMPLE 1

In this example (simulated) Bisphenol A Polycarbonate (BPA-PC) wasretained as the substrate material, while isophthalate terephthalateresorcinol-polycarbonate (ITR-PC 80-20) blend, styrene acrylonitrile(SAN 576) or BPA-PC was chosen as the optical film. The optical film hasa thickness of about 100 micrometers while the substrate has a thicknessof 1.1 millimeters giving a film to substrate thickness ratio of 0.09.

Both the substrate and optical film stiffness were measured in tensiledeformation at room temperature using an Instron tensile testingmachine. The swell of a polymeric material as defined herein is thepercentage of volume growth of the totally dry material when subjectedto a 100% relative humidity environment at a specific temperature. Theswell is measured utilizing a TMA 2940 Thermomechanical Analyzer from TAinstruments. A film is mounted under a very low constant load andinitially held in a dry atmosphere. The length change is then measuredupon absorption of water when the material is exposed to 100% relativehumidity. The water strain or swell is taken to be the strain of thematerial (length change divided by the original gauge length).

Table 2 below outlines the stiffness and swell ratio of the film tosubstrate as well as the radial tilt range for the different materialcombinations. It can be clearly seen that when polymeric materialschosen for the optical film and the substrate are different from eachother, the radial tilt range is much smaller than for the purely matchedmaterial system where BPA-PC alone is used as material for the substrateand optical film

TABLE 2 Stiffness ratio Swell ratio Radial Tilt Range Film Material(film to substrate) (film to substrate) (degrees) ITR-PC 80-20 1.1011.781 0.292 SAN 576 1.378 1.649 0.236 BPA-PC 1.000 1.000 0.560

Generally an optical film that is stiffer and has a greater swell (waterstrain) than the substrate material will have better performance whencompared to a matched film/substrate system.

EXAMPLE 2

In this example BPA-PC is the polymeric material used for the opticalfilm and different polymeric materials were used as the substrate asshown in Table 2. The optical film has a thickness of about 100micrometers while the substrate has a thickness of 1.1 millimetersgiving a film to substrate thickness ratio of 0.09. The substratematerials are listed as follows: copolyester polycarbonate of BisphenolA and dodecanoic acid containing 7 mole % of polyester and 93 mole % ofBPA-PC (RL-7553), 39 mole % of polyphenylene ether and 61 mole %polystyrene (PPE/PS 101), 1,3-bis(4-hydroxyphenyl methane) (BHPM), 90mole % bisphenol A and 10 mole % disecbutyl bisphenol A (BPA disecbutylBPA), polycarbonate of tetramethyl cyclobutanediol (TMCBD-PC) and blendof BPA-polycarbonate with polycarbonate tetra xylyl hydroquinonediphosphite (BPA-PC+1 wt % TXHQDR).

TABLE 3 Stiffness ratio Swell ratio Radial Tilt (film to (film to RangeSubstrate Material substrate) substrate) (degrees) RL 7553 (SPOQ) 1.3111.209 0.297 PPE/PS 101 0.744 2.141 0.196 39%/61% BHPM 1.000 1.724 0.208BPA-disecbutyl 0.908 1.560 0.284 BPA 90-10 TMCBD-PC 1.478 2.451 0.167BPA-PC + 1 wt % 1.188 1.200 0.339 TXHQDP BPA-PC 1.000 1.000 0.560

Both the substrate and optical film stiffness were measured in tensiledeformation at room temperature using an Instron tensile testingmachine. The swell of a polymeric material as defined herein is thepercentage of volume growth of the totally dry material when subjectedto a 100% relative humidity environment at a specific temperature. Theswell is measured utilizing a TMA 2940 Thermomechanical Analyzer from TAinstruments. A film is mounted under a very low constant load andinitially held in a dry atmosphere. The length change is then measuredupon absorption of water when the material is exposed to 100% relativehumidity. The water strain or swell is taken to be the strain of thematerial (length change divided by the original gauge length). Table 3above outlines the stiffness and swell ratio of the film to substrate aswell as the radial tilt range for the different material combinations.Once again it can be seen that when the polymeric material used as theoptical film differs from that used for the substrate, the radial tiltrange is significantly decreased which in turn allows for the increasedstorage capacity.

EXAMPLE 3

In this example, BPA-PC was replaced in both the optical film andsubstrate by different materials as indicated in Table 4 below. Theoptical film has a thickness of about 100 micrometers, while thesubstrate has a thickness of 1.1 millimeter giving a film to substratethickness ratio of 0.09.

TABLE 4 Stiffness ratio Swell ratio Radial Tilt Film Substrate (film to(film to Range Material Material substrate) substrate) (degrees) PS 101PPE/PS 101 1.039 0.010 0.154 39%/61% BHPM PPE/PS 101 1.000 2.935 0.14239%/61%

Here the optical film was polystyrene (PS) in one case while1,3-bis(4-hydroxyphenyl methane) (BHPM) was used in the other. A blendof 39 mole % of polyphenylene ether and 61 mole % polystyrene was usedas the substrate in both cases. Both the substrate and optical filmstiffness were measured in tensile deformation at room temperature usingan Instron tensile testing machine. The swell of a polymeric material asdefined herein is the percentage of volume growth of the totally drymaterial when subjected to a 100% relative humidity environment at aspecific temperature. The swell is measured utilizing a TMA 2940Thermomechanical Analyzer from TA instruments. A film is mounted under avery low constant load and initially held in a dry atmosphere. Thelength change is then measured upon absorption of water when thematerial is exposed to 100% relative humidity. The water strain or swellis taken to be the strain of the material (length change divided by theoriginal gauge length). Table 4 above outlines the stiffness and swellratio of the film to substrate as well as the radial tilt range for thedifferent material combinations. Once again it can be seen that when thepolymeric material used as the optical film differs from that used forthe substrate, the radial tilt range is significantly decreased which inturn allows for the increased storage capacity.

The storage media disclosed herein reduces radial tilt by mismatchingthe compositions of the optical film and substrate, and by optionallyemploying mis-matched thicknesses of the substrate and optical film. Themis-matched compositions contribute in enabling higher areal densitystorage (about 20 GB or greater) when compared to a dice without amis-matched composition of the optical film and the substrate.

While the invention has been described with reference to an exemplaryembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A storage media, comprising: a plastic substrate having a substratecomposition and a substrate thickness; an optical layer having a layercomposition different from the substrate composition; a data storagelayer disposed therebetween; and a reflective layer disposed between thedata storage layer and the substrate; wherein the storage media has aradial deviation over time of less than or equal to about 1.15 degreesat a radius of 55 mm when exposed in humidity.
 2. The storage media ofclaim 1, wherein a stiffness ratio of the optical layer to the substrateis about 0.5 to about 5 measured in tensile deformation at roomtemperature.
 3. The storage media of claim 2, wherein the stiffnessratio is about 0.7 to about 3 measured in tensile deformation at roomtemperature.
 4. The storage media of claim 3, wherein the stiffnessratio is about 1.25 to about 2.5 measured in tensile deformation at roomtemperature.
 5. The storage media of claim 1, wherein a swell ratio ofthe optical layer to the substrate is about 0.5 to about 5.0.
 6. Thestorage media of claim 5, wherein the swell ratio is about 0.75 to about3.0.
 7. The storage media of claim 6, wherein the swell ratio is about1.0 to about 2.5.
 8. The storage media of claim 1, wherein the opticallayer has a layer thickness of greater than or equal to about 20% of thesubstrate thickness.
 9. The storage media of claim 8, wherein the layerthickness is about 20% to about 40% of the substrate thickness.
 10. Thestorage media of claim 9, wherein the layer thickness is about 25% toabout 35% of the substrate thickness.
 11. The storage media of claim 1,wherein the optical layer has a layer thickness of about 0.2 micrometersto about 0.6 mm.
 12. The storage media of claim 11, wherein the layerthickness is about 0.2 micrometers to about 120 micrometers.
 13. Thestorage media of claim 1, wherein the substrate thickness is about 0.3mm to about 2.5 mm.
 14. The storage media of claim 13, wherein thesubstrate thickness is about 0.6 mm to about 2.0 mm.
 15. The storagemedia of claim 14, wherein the substrate thickness is about 1.1 mm about1.5 mm.
 16. The storage media of claim 1, wherein the optical layer hasa layer thickness, and a thickness ratio of the layer thickness to thesubstrate thickness is about 0.001 to less than
 1. 17. The storage mediaof claim 16, wherein thickness ratio is about 0.005 to about 0.5. 18.The storage media of claim 17, wherein the thickness ratio is about0.025 to about 0.1.
 19. The storage media of claim 1, wherein the layercomposition and the substrate composition are plastics individuallyselected from the group consisting of thermoplastics, thermosets, andhomopolymers, copolymers, reaction products, and combinations comprisingat least one of the foregoing plastics.
 20. The storage media of claim19, wherein the thermoplastics are selected from the group consisting ofpolyethylene, polypropylene, copolymers of polyethylene andpolypropylene, chlorinated polyethylene, polyvinyl chloride,polymethylpentane; ethylene-tetrafluoroethylene copolymers, polyvinylfluoride, polyvinylidene fluoride, polyvinylidene chloride,polytetrafluoroethylene, ethylene-vinyl acetate copolymers, polyvinylacetate, diene-derived polymers and copolymers, polybutadiene,polyisoprene, polymers of ethylenically unsaturated carboxylic acids,functional derivatives of polymers containing ethylenically unsaturatedcarboxylic acids, acrylic polymers, poly(alkyl acrylates), poly(alkylmethacrylates), polyacrylamides, polyacrylonitrile, polyacrylic acid,alkenylaromatic polymers, polystyrene, poly-alpha-methylstyrene,hydrogenated polystyrenes, syndiotactic and atactic polystyrenes,polycyclohexyl ethylene, styrene-co-acrylonitrile, styrene-co-maleicanhydride, polyvinyltoluene, rubber-modified polystyrenes; polyamides,nylon-6, nylon-66, nylon-11 and nylon-12, polyacetals, polyesters,polyethylene terephthalate, polybutylene terephthalate,polycyclohexylmethylene terephthalate, polycarbonates,polyestercarbonates, high heat polycarbonates, polyethers, polyaryleneethers, polyphenylene ethers derived from 2,6-dimethylphenol andcopolymers with 2,3,6-trimethylphenol, polyethersulfones,polyetherethersulfones, polyetherketones, polyetheretherketones, andpolyetherimides, polyarylene sulfides, polysulfones, andpolysulfidesulfones, liquid crystalline polymers and homopolymers,copolymers, reaction products, combinations and composites comprising atleast one of the foregoing thermoplastics, and wherein the thermosettingresins are selected from the group consisting epoxies, phenolics,alkyds, polyesters, polyimides, polyurethanes, mineral filled silicones,bis-maleimides, cyanate esters, multifunctional allylic compounds,acrylics, alkyds, phenol-formaldehyde, novolacs, resoles, bismaleimides,melamine-formaldehyde, urea-formaldehyde, benzocyclobutanes,hydroxymethylfurans, isocyanates, benzocyclobutene resins, andhomopolymers, copolymers, reaction products, and combinations comprisingat least one of the foregoing thermosetting resins.
 21. The storagemedia of claim 1, wherein the radial deviation is less than or equal toabout 1.0 degrees.
 22. The storage media of claim 21, wherein the radialdeviation is less than or equal to about 0.7 degrees.
 23. The storagemedia of claim 22, wherein the radial deviation it less than or equal toabout 0.5 degrees.
 24. The storage media of claim 23, wherein the radialdeviation is less than or equal to about 0.25 degrees.
 25. A storagemedia comprising: a plastic substrate having a substrate composition anda substrate thickness; an optical layer having a layer composition and alayer thickness, wherein the layer thickness differs from the substratethickness and the layer composition differs from the substratecomposition; a data storage layer disposed therebetween; and areflective layer disposed between the data storage layer and thesubstrate; wherein the storage media has a radial deviation over time ofless their or equal to about 1.15 degrees at a radius of 55 mm whenexposed to humidity.
 26. The storage media of claim 25, wherein astiffness ratio of the optical layer to the substrate is about 0.5 toabout 5 measured in tensile deformation at room temperature.
 27. Thestorage media of claim 26, wherein the stiffness ratio is about 0.7 toabout 3 measured in tensile deformation at room temperature.
 28. Thestorage media of claim 27, wherein the stiffness ratio is about 1.25 toabout 2.5 measured in tensile deformation at room temperature.
 29. Thestorage media of claim 25, wherein a swell ratio of the optical layer tothe substrate is about 0.5 to about 5.0.
 30. The storage media of claim29, wherein the swell ratio is about 0.75 to about 3.0.
 31. The storagemedia of claim 30, wherein the swell ratio is about 1.0 to about 2.5.32. The storage media of claim 25, wherein the layer thickness isgreater than or equal to about 20% of the substrate thickness.
 33. Thestorage media of claim 32, wherein the layer thickness is about 20% toabout 40% of the substrate thickness.
 34. The storage media of claim 33,wherein the layer thickness is about 25% to about 35% of the substratethickness.
 35. The storage media of claim 34, wherein the layercomposition and the substrate composition are plastics individuallyselected from the group consisting of thermoplastics, thermosets, andhomopolymers, copolymers, reaction products, end combinations comprisingat least one of the foregoing plastics.
 36. The storage media of claim25, wherein the radial deviation is less than or equal to about 1.0degrees.
 37. The storage media of claim 36, wherein the radial deviationis less than or equal to about 0.7 degrees.
 38. The storage media ofclaim 37, wherein the radial deviation is less than or equal to about0.5 degrees.
 39. The storage media of claim 38, wherein the radialdeviation is less than or equal to about 0.25 degrees.
 40. A storagemedia, comprising: a plastic substrate having a substrate compositionand a substrate thickness; an optical layer having a layer compositiondifferent from the substrate composition; a data storage layer disposedtherebetween; and a reflective layer disposed between the data storagelayer and the substrate; wherein the storage media has a radialdeviation over time of less than or equal to about 1.15 degrees ateradius of 55 mm when exposed to humidity, a stiffness ratio of theoptical layer to the substrata is about 0.5 to about 5 measured intensile deformation at room temperature, a swell ratio of the opticallayer to the substrate is about 0.5 so about 5.0.
 41. The storage mediaof claim 40, wherein the stiffness ratio is about 0.7 to about 3measured in tensile deformation at room temperature.
 42. The storagemedia of claim 41, wherein the stiffness ratio is about 1.25 to about2.5 measured in tensile deformation at room temperature.
 43. The storagemedia of claim 40, wherein the swell ratio is about 0.75 to about 3.0.44. The storage media of claim 43, wherein the swell ratio is about 1.0to about 2.5.
 45. The storage media of claim 1, wherein the substratecomprises a thermoset and the optical layer comprises a thermoplastic.46. The storage media of claim 1, wherein the radial deviation over timeof less than or equal to about 1.15 degrees at a radius of 55 mm, whenexposed to a cycle at 25° C. of 50% relative humidity—90% relativehumidity—50% relative humidity.
 47. The storage media of claim 25,wherein the substrate comprises a thermoset and the optical layercomprises a thermoplastic.
 48. The storage media of claim 25, whereinthe radial deviation over time of less than or equal to about 1.15degrees at a radius of 55 mm, when exposed to a cycle at 25° C. of 50%relative humidity—90% relative humidity—50% relative humidity.
 49. Thestorage media of claim 40, wherein the substrate comprises a thermosetand the optical layer comprises a thermoplastic.
 50. The storage mediaof claim 40, wherein the radial deviation over rime of less than orequal to about 1.15 degrees at a radius of 55 mm, when exposed to acycle at 25° C. of 50% relative humidity—90% relative humidity—50%relative humidity.
 51. The storage media of claim 20, wherein the layercomposition and the substrate composition are, individually, selectedfrom the group consisting of polycarbonate, polyarylene ether,polystyrene, poly(alkyl acrylate), and copolymers and combinationscomprising at least one of the foregoing.
 52. The storage media of claim1, wherein at least one of the layer composition comprise residues of1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane.
 53. A storage media,comprising: a plastic substrate having a substrate compositioncomprising a polyaryleae ether and having a substrate thickness; anoptical layer having an optical layer composition different from thesubstrate composition; a reflective layer disposed between the opticallayer and the substrate; wherein the storage media has a radialdeviation over time of less than or equal to 1.15 degrees at a radius of55 mm when exposed to a cycle at 25° C. of 50% relative humidity—90%relative humidity—50% relative humidity and wherein the storage media iscapable of storing greater than or equal to about 20 GB of data.
 54. Thestorage media of claim 53, wherein the substrate has a side comprisingsurface features, and wherein the reflective layer is disposed on theside of the substrate comprising the surface features.
 55. The storagemedia of claim 53, further comprising a data storage layer disposedbetween the reflective layer and the optical layer, wherein the datastorage layer comprises a material selected from the group consisting ofan organic dye and an inorganic phase change compound.
 56. The storagemedia of claim 53, wherein a stiffness ratio of the optical layer to thesubstrate is about 0.5 to about 5 measured in tensile deformation atroom temperature.
 57. The storage media of claim 53, wherein a swellratio of the optical layer to the substrate is about 0.5 to about 5.0.58. The storage media of claim 53, wherein the optical layer thicknessis about 0,2 micrometers to about 120 micrometers.
 59. The storage mediaof claim 53, wherein the optical layer composition is selected from thegroup consisting of polycarbonates, acrylic polymers, epoxies,silicones, and copolymers and combinations comprising at least one ofthe foregoing optical layer compositions.
 60. The storage media of claim59, wherein the optical layer composition comprises poly(alkylacrylate).
 61. The storage media of claim 59, wherein the opfical layercomposition comprises silicones.
 62. The storage media of claim 53,wherein the substrate composition further comprises polystyrene.
 63. Thestorage media of claim 62, wherein the polyarylene ether comprises apolyphenylene ether selected front the group consisting of polyphenyleneether derived from 2,6- dimethylphenol, polyphenylene ether derived from2,6-dimethylphenol copolymerized with 2,3,6-trimethylphenol, andreaction products, combinations, and composites comprising at least oneof the foregoing polyphenylene ethers.
 64. The storage media of claim53, wherein the radial deviation is less than or equal to about 1.0degree.
 65. The storage media of claim 64, wherein the radial deviationis less than or equal to about 0.5 degrees.
 66. The storage media ofclaim 53, further comprising a dielectric layer disposed between theoptical layer and the substrate, wherein the dielectric layer isselected from the group consisting of silicon nitride, aluminum nitride,aluminum oxide, silicon carbide, and combinations comprising at leastone of the foregoing dielectric layers.
 67. The storage media of claim53, further comprising an adhesive layer disposed between the opticallayer and the substrate, wherein the adhesive layer is selected from thegroup consisting of polyisoprene, styrene butadiene rubber, ethylenepropylene rubber, fluoro vinyl methyl siloxane, chlorinatedisobutene-isoprene, chloroprene, chlorinated polyethylene,chlorosulfonated polyethylene, butyl acrylate, expanded polystyrene,expanded polyethylene, expanded polypropylene, foamed polyurethane,plasticized polyvinyl chloride, dimethyl silicone polymers, methyl vinylsilicone, polyvinyl acetate, and combinations comprising at least one ofthe foregoing adhesives.
 68. The storage media of claim 53, furthercomprising an adhesive layer disposed between the optical layer and thesubstrate, wherein the adhesive layer is selected from the groupconsisting of a UV curable adhesive, a pressure sensitive adhesive, andcombinations comprising at least one of the foregoing.
 69. The storagemedia of claim 53, further comprising a lubrication layer, wherein thelubrication layer is selected from the group consisting of fluoro oils,and fluoro greases, and combinations comprising at least one of theforegoing.
 70. The storage media of claim 53, wherein the optical layercomposition is selected from the group consisting ofethylene-tetrafluoroethylene copolymers, polyvinyl fluoride,polyvinylidene fluoride, polyvinylidene chloride, andpolytetrafluoroethylene, and reaction products, and combinationscomprising at least one of the foregoing optical layer compositions. 71.A storage media, comprising: a plastic substrate having a substratecomposition comprising a polyarylene ether and having a substratethickness; an optical layer bring an optical layer composition differentfrom the substrate composition; and wherein the storage media has aradial deviation over time of less than or equal to about 1.15 degreesat a radius of 55 mm when exposed to humidity, a stiffness ratio of theoptical layer to the substrate of about 0.5 to about 5 measured intensile deformation at room temperature, a swell ratio of the opticallayer to the substrate of about 0.5 to about 5.0; and wherein thestorage media is capable of storing greater than or equal to about 20 GBof data; and wherein the storage media is capable of reflecting anenergy field.
 72. The storage media of claim 71, further comprising areflective layer disposed between the optical layer and the substrate,and wherein the substrate has a side comprising surface features, andwherein the reflective layer is disposed on the side of the substratecomprising the surface features.
 73. The storage media, of claim 71,wherein a stiffness ratio of the optical layer to the substrate is about0.5 to about 5 measured in tensile deformation at room temperature. 74.The storage media of claim 71, wherein a swell ratio of the opticallayer to the substrate is about 0.5 to about 5.0.
 75. The storage mediaof claim 71, wherein the optical layer thickness is about 0.2micrometers to about 120 micrometers.
 76. The storage media of claim 71,wherein the optical layer composition is selected from the groupconsisting of polycarbonates, acrylic polymers, epoxies, silicones, andcopolymers and combinations comprising at least one of the foregoingoptical layer compositions.
 77. The storage media of claim 71, whereinthe optical layer composition comprises poly(alkyl acrylate).
 78. Thestorage media of claim 71, wherein the optical layer compositioncomprises silicones.
 79. The storage media of claim 71, wherein thesubstrate composition further comprises polystyrene.
 80. The storagemedia of claim 71, wherein the polyarylene ether comprises apolyphenylene ether selected from the group consisting of polyphenyleneether derived from 2,6- dimethylphenol, polyphenylene ether derived from2,6-dimethylphenol copolymerized with 2,3,6-tyimethylphenol, andreaction products, combinations, and composites comprising at least oneof the foregoing polyphenylene ethers.
 81. The storage media of claim71, wherein to radial deviation is less than or equal to about 1.0degree.
 82. The storage media of claim 71, wherein the optical layercomposition is selected from the group consisting ofethylene-tetrafluoroethylene copolymers, polyvinyl fluoride,polyvinylidene fluoride, polyvinylidene chloride, andpolytetrafluoroethylene, and reaction products, and combinationscomprising at least one of the foregoing optical layer compositions. 83.The storage media of claim 81, wherein the radial deviation is less thanor equal to about 0.5 degrees.